Cesium sorption

Fig. 8.37 Cesium sorption on Bure mudrock samples as a function of concentration in solution at equilibrium, at four different depths (Melkior et al. 2005)...

When preparing the cesium- and barium-saturated clays, the 1.0 M solutions used were decanted (after centrifuging) and analyzed semiquantitatively by emission spectroscopy. From those analyses, it appears that the following species were desorbed sodium, potassium, calcium, magnesium, and strontium. It further appeared that desorption of potassium was almost unique to cesium sorption whereas, desorption of the other species appeared to be common to both cesium and barium sorption. Small amounts of other elements such as nickel and copper were also detected by the analyses. However, to what extent the observed concentrations may represent desorption and to what extent they may represent the dissolution of sparingly soluble substances (particularly hydroxide species) is as yet-uncertain. The apparent concentrations of the desorbed species per gram of clay are given in Table III. 

Todd, T.A., Mann, N.R., Tranter, T.J., Sebesta, F., John, J., Motl, A. Cesium sorption from concentrated acidic tank wastes using ammonium molybdophosphate-polyacrylo-nitrile composite sorbents. J. Radioanal. Nucl. Chem. (2002), 254 (1), 47-52. 

Table VII shows that for cesium sorption, both KC1 and N H4 are significant for the two geologic solids studied. The negative values indicate that the presence of either KC1 or lowers sorption. Both appear to be competing with Cs+ ion for sorption sites. Competition between K+ and Cs+ ions for sorption sites on mica-like minerals is well known. However, displacement of Cs+ by hydrazine was surprising since N H, should exist mainly as a neutral species at pH 9-10. A small amount (0.0005M to 0.005M) will be protonated and apparently competes with Cs+. Ammonium ion is known to effectively compete with Cs+ for mineral sorption sites. Hydrazinium ion with a similar molecular structure should also displace Cs+. Since hydrazine will not reduce or complex Cs+, the only possible effects on cesium sorption is to compete for sorption sites or to alter the surface of the solid minerals. No evidence of surface alteration (change in color or texture) was observed. Therefore, it appears that an Eh buffer is not required for Cs+ sorption studies and hydrazine only interferes with the sorption reaction.

Using the criteria referred to in the introductory section, the deposition rate constants given in Table II can be used to estimate transit times necessary to achieve equilibrium in laboratory or field fracture flow studies For example cesium sorption from GGW in a 100-ym aperture fissure in unweathered Lac du Bonnet granite requires a minimum water transit time of 3 d for site 1, and 12 d for site 2, in order to be able to assume equilibrium sorption. Water transit times of the order of hours will produce only tailing. Transit times required in brine groundwaters are an order of magnitude higher than those in GGW. 

Another phyllosilicate mineral, namely, biotite, has larger sorption capability as expected. It is likely related to the iron content of biotite. Similarly, the carbonates containing iron and magnesium (ankerite and dolomite Table 3.8) show more significant cesium sorption as calcite (calcium carbonate), which practically does not adsorb cesium. The low sorption ability of calcite can be explained by the Hahn adsorption rule (Chapter 1, Section 1.2.4) that is, the sorption is low when the sorbate (cesium carbonate) has great solubility. 

Cygan, R. T., Nagy, K. L., and Brady, P. V. (1998). Molecular models of cesium sorption on kaolinite. In Adsorption of Metals by Geomedia Variables, Mechanisms, and Model Applications, ed. Jenne, E. A., Academic Press, San Diego, CA, 383-399. 

Rajec, P., Sucha, V., Eberl, D. D., Srodon, J., and Elsass, F. (1999). Effect of illite particle shape on cesium sorption. Clays Clay Miner. 47, 755-760. 

Tamura, T., and Jacobs D. G., (1960). Structural implications in cesium sorption. Health Phys. 2, 391-398. 

Sawhney, B.L. 1966. Kinetic of cesium sorption by clay minerals. Soil Sci. Soc. Am. Proc, 30 565-569. 

The fit of the 3-box model to the sediment data is slightly better, particularly for the first 48 hours. Again, readsorption is predicted for the desorption period, albeit slightly less than the extent predicted by the 2-box model. However, one might argue whether the addition of a fifth fitting parameter in the model is statistically justified for the data of cesium sorption to sediments. 

Hydrothermal effects on cesium sorption and fixation by clay minerals and shales. Clays Clay Miner., 28,142-148. 

Comans, R.N.J., and D.E. Hockley. 1992. Kinetics of cesium sorption on illite. Geochim. Cosmochim. Acta 56 1157-1164. 

Cygan, R.T., K.L. Nagy, and P.V. Brady. 1998. Molecular models of cesium sorption on kaolinite. p. 383-399. In E.A. Jenne (ed.) Sorption of metals by earth materials. Academic Press, New York. 

The effect of collapse-inducing cations on the cesium sorption properties of hydrobiotite. 

Cesium sorption reactions as indicator of clay mineral structures. Clays Clay Min. 

---